FIG. 4 is a sectional view illustrating an existing double cavity-type toroidal continuously variable transmission used as a transmission for a vehicle, and FIG. 5 is an enlarged sectional view of the main parts thereof. This toroidal continuously variable transmission 1 is assembled into a casing 2.
The toroidal continuously variable transmission 1 includes input side discs 4A and 4B which are provided in the periphery of an input shaft (variator shaft) 3 to rotate along with the input shaft 3 and are supported to be displaced in the axial direction of the input shaft 3, and an integrated type output side disc 10 which are rotatably supported. A radial bearing 7 is interposed between the output side disc 10 and the input shaft 3, and the position of the output side disc 10 in the axial direction is determined by thrust bearings 12 and 12 provided at both end portions thereof in the axial direction. In addition, the output side disc 10 is rotatably supported by the radial bearing 7 and the thrust bearings 12.
As illustrated in FIG. 6, in the casing 2 in which the toroidal continuously variable transmission 1 is stored, a pair of trunnions 6 and 6 which oscillate about pivots (tilt axes) 5 and 5 which are provided at positions where they twist with respect to the input shaft 3 are provided. Each of the trunnions 6 has a concave pocket portion P, and a power roller 11 is accommodated in the pocket portion P.
A circular hole is formed in the trunnion 6, and a base end portion 9a of a displacement shaft 9 is supported in the circular hole. In addition, by allowing the trunnions 6 and 6 to respectively oscillate about the pivots 5 and 5, the tilt angles of the displacement shafts 9 respectively supported by the center portions of the trunnions 6 and 6 can be controlled. In the periphery of a tip end portion 9b of the displacement shaft 9 which protrudes from the inner surface of each of the trunnions 6 and 6, the power roller 11 is rotatably supported, and the power rollers 11 and 11 are respectively interposed between the input side discs 4A and 4B and the output side disc 10. The base end portion 9a and the tip end portion 9b of each of the displacement shafts 9 and 9 are mutually eccentric.
Both end portions of the pair of trunnions 6 and 6 are supported to be displaced in the axial direction (up and down direction in FIG. 6) while being able to oscillate with respect to a pair of yokes 23A and 23B. The yokes 23A and 23B are supported by a pair of posts 61 and 61. That is, the post 61 is a support provided perpendicular to the input shaft 3 in the casing 2, and the upper yoke 23A is supported to be displaced by a spherical post 64 of the post 61 and a connection plate 65 which supports the spherical post 64. The lower post 23B is supported to be displaced by a spherical post 68 of the post 61 and an upper cylinder body 60 which supports the spherical post 68.
The input shaft 3 is inserted through the center portion of the post 61. That is, as illustrated in FIGS. 5 and 6, an insertion hole 62 is formed in the center portion of the post 61. The insertion hole 62 includes a large-diameter hole 62a, and a fitting hole 62b which has a smaller diameter than the large-diameter hole 62a. 
In addition, the thrust bearing 12 is inserted through the insertion hole 62, and one bearing ring 12a of the thrust bearing 12 is fitted into the fitting hole 62b. An end portion 10b of the output side disc 10 is inserted through the large-diameter hole 62a of the insertion hole 62, and the other bearing ring 12b of the thrust bearing 12 inserted through the large-diameter hole 62a is fitted to the end portion 10b. 
Accordingly, the input shaft 3 is inserted through the inside of the thrust bearing 12 fitted in the post 61, and a predetermined gap is formed between the input shaft 3 and the inner peripheral surface of the thrust bearing 12.
As illustrated in FIG. 6, between the outer surface of each of the power rollers 11 and 11 and each of the trunnions 6 and 6, a thrust ball bearing 24 and a thrust needle bearing 25 are provided in order from the outer surface of the power roller 11. Among these, the thrust ball bearing 24 allows the rotation of the corresponding power roller 11 while withstanding a load in the thrust direction applied to the power roller 11.
In addition, the thrust needle bearing 25 allows the oscillation and displacement of the corresponding power roller 11 and an outer race 28 about the base end portion 9a of the corresponding displacement shaft 9 while withstanding a thrust load applied from the power roller 11 to the outer race 28.
Furthermore, in one end portion (lower end portion in FIG. 6) of each of the trunnions 6 and 6, a driving rod (trunnion shaft) 29 is provided, and a driving piston (hydraulic piston) 30 is fixed to the outer peripheral surface of the intermediate portion of each of the driving rods 29. Each of the driving pistons 30 is oil-tightly embedded in a driving cylinder 31 to form a hydraulic driving device. In this case, the driving cylinder (cylinder body) 31 is formed by the upper cylinder body 60 and a lower cylinder body 66.
In addition, as illustrated in FIG. 4, a crankshaft of an engine which is a driving source (not illustrated) is joined to the base end portion (left end portion in FIG. 4) of the input shaft 3 via a driving shaft 72, and the tip end portion (right end portion in FIG. 4) of the input shaft 3 is rotatably supported by a bearing 73 provided in the casing 2. The input shaft 3 is rotatingly drived by the crankshaft via the driving shaft 72.
In addition, hydraulic pressing devices 23a for applying appropriate surface pressures to rolling contact portions (traction portions) between inner surfaces 4a and 4b of both the input side discs 4A and 4B, both side surfaces (inner surfaces) 10a and 10a of the output side disc 10 in the axial direction, and an peripheral surface 11a of each of the power rollers 11 and 11 are used. Pressure oil can be supplied by an oil pump (not illustrated) to the pressing devices 23a and the driving cylinders 31 for displacing the trunnions 6 and 6 to change the speed.
In the toroidal continuously variable transmission 1 assembled in such a continuously variable transmission, in the case of changing the ratio of the rotational speeds of the input shaft 3 and the output side disc 10, the pair of driving pistons 30 and 30 are displaced in the opposite directions to each other. As the driving pistons 30 and 30 are displaced, the pair of trunnions 6 and 6 are displaced in the opposite directions to each other. As a result, the directions of forces in the normal direction exerted on the contact portions between the peripheral surfaces 11a and 11a of the power rollers 11 and 11, the inner surfaces 4a and 4b of the input side discs 4A and 4B, and both side surfaces 10a and 10a of the output side disc 10 in the axial direction are changed. As the directions of the forces are changed, the trunnions 6 and 6 respectively oscillate in the opposite directions to each other about the pivots 5 and 5 pivotally supported on the yokes 23A and 23B.
As a result, the contact positions between the peripheral surfaces 11a and 11a of the power rollers 11 and 11 and the inner surfaces 4a, 4b, and 10a are changed such that the ratio of the rotational speeds of the input shaft 3 and the output side disc 10 is changed. When the torque transmitted between the input shaft 3 and the output side disc 10 is changed and thus the elastic deformation amount of each of the constituent members is changed, the power rollers 11 and 11 and the outer races 28 attached to the power rollers 11 slightly rotate about the base end portions 9a of the corresponding displacement shafts 9. Since the thrust needle bearing 25 is present between the outer surface of the corresponding outer race 28 and the corresponding trunnion 6, the rotation is smoothly performed. However, as described above, a force for changing the tilt angle of each of the displacement shafts 9 and 9 is small.